The present invention is related to satellite communications in general and, more specifically, to determining acquisition guard times for very small aperture terminal (VSAT) networks utilizing a time-division multiple access (TDMA) technique. When a terminal enters a TDMA network, the terminal typically needs to synchronize its transmit timing to a TDMA network frame timing to avoid transmission overlap with existing bursts. Since a terminal may not have precise knowledge of its transmit frame timing, a large guard time (larger than that required during steady-state synchronization) is allocated to the terminal. An acquisition guard time may be based on a worst-case acquisition guard time for a network. This may be computed from the satellite motion as determined by its inclination, east-west drift and eccentricity, and the geographical coverage of a network. In addition, an acquisition control parameter may be computed for each terminal based on the terminal's coordinates and the nominal or approximate satellite position.
While these techniques for determining acquisition guard time may be simple, they may result in a large acquisition guard time, in particular for a large orbit inclination. For example, for a satellite system with global coverage, a typical acquisition guard time may be from 0.5 ms to 35 ms, depending on orbit inclination. In some cases, an acquisition guard time may actually be larger than the frame time.
Acquisition guard time may be reduced by determining a satellite position more accurately, but this generally involves utilizing an external system, such as telemetry, tracking and control (TTC) stations, and satellite operations centers (SOCs). It may be beneficial for there to be new systems and methods, which may be based on internal network functions, to more accurately and/or efficiently determine satellite positions and to compute acquisition control parameters for terminals to reduce acquisition guard time.